A force-sensitive resistor (FSR) assembly includes first and second electrically insulative substrates. The first substrate includes a first top surface and a first bottom surface. The second substrate includes a second top surface and a second bottom surface. The first substrate is positioned such that the first bottom surface is disposed facing the second top surface. The FSR assembly also includes thermoset ink disposed between the first substrate and the second substrate.
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1. A force-sensitive resistor (FSR) assembly, comprising: a first substrate made from a polyimide material having a decomposition temperature greater than or equal to approximately 300° Celsius and a coefficient of thermal expansion less than or equal to approximately 30, the first substrate having a first top surface and a first bottom surface opposite the first top surface; a second substrate made from the polyimide material, the second substrate having a second top surface and a second bottom surface opposite the second top surface; a first thermoset ink disposed on a portion of the first bottom surface; a second thermoset ink disposed on a portion of the second top surface, wherein the first substrate is positioned such that the portion of the first bottom surface faces the portion of the second top surface, and the first thermoset ink or the second thermoset ink comprising at least one of carbon black particles or silver particles; and an adhesive disposed between the first substrate and the second substrate, wherein the first thermoset ink and the second thermoset ink are disposed radially inward of the adhesive along an axis of the FSR assembly extending substantially parallel to at least one of the first bottom surface and the second top surface, and the adhesive is configured to separate the first thermoset ink from the second thermoset ink by a distance.
A force-sensitive resistor (FSR) assembly comprises two substrates made of polyimide with a decomposition temperature of at least 300°C and a thermal expansion coefficient of at most 30. The first substrate has a top and bottom surface, as does the second. A thermoset ink is on a portion of the first substrate's bottom surface, and another thermoset ink is on a portion of the second substrate's top surface, facing each other. At least one ink contains carbon black or silver particles. An adhesive separates the substrates, positioned radially outward from the inks. The adhesive creates a gap between the two ink portions.
2. The assembly of claim 1 , further comprising a plurality of conductors disposed on the second top surface, and a dielectric material disposed on at least one conductor of the plurality of conductors, the dielectric material being disposed between the adhesive and the second bottom surface.
The FSR assembly as described previously also includes multiple conductors on the second substrate's top surface. A dielectric material covers at least one of these conductors. This dielectric is positioned between the adhesive and the second substrate's bottom surface, providing insulation and preventing electrical shorts.
3. The assembly of claim 1 , wherein the first thermoset ink comprises carbon black particles and the second thermoset ink comprises silver particles, the assembly further including a layer of carbon material disposed between the second thermoset ink and the first thermoset ink.
The FSR assembly as described previously utilizes carbon black particles in the first thermoset ink and silver particles in the second thermoset ink. A layer of carbon material is positioned between the silver-containing ink and the carbon black-containing ink, possibly to modify the electrical characteristics or improve the contact between the layers.
4. The assembly of claim 1 , the first substrate having a first thickness and the second substrate having a second thickness less than the first thickness, the carbon black particles having a particle size between approximately 70 nanometers and approximately 2 micrometers, and the silver particles having a particle size between approximately 70 nm and approximately 2 micrometers.
The FSR assembly as described previously has a first substrate that is thicker than the second substrate. The carbon black and silver particles used in the thermoset inks each have a particle size between 70 nanometers and 2 micrometers. This size range optimizes the force-sensing characteristics of the FSR.
5. The assembly of claim 1 , wherein a force concentration layer is disposed on the first top surface and a preload layer is disposed on the force concentration layer, the preload layer applying a preload force to at least the first substrate, via the force concentration layer, of between approximately 100 gram force and approximately 500 gram force in the absence of other external forces applied to the first substrate.
The FSR assembly as described previously incorporates a force concentration layer on top of the first substrate and a preload layer on top of the force concentration layer. The preload layer applies a constant force between 100 and 500 gram-force to the first substrate via the force concentration layer even when no external force is applied. This ensures consistent sensitivity and response of the FSR.
6. An electronic device, comprising: a processor; a display coupled to the processor; memory coupled to the processor; and a force-sensitive resistor (FSR) assembly coupled to the processor, the FSR assembly including: a first substrate comprising an electrically insulative material, the first substrate having a first top surface and a first bottom surface opposite the first top surface, a second substrate including the electrically insulative material, the second substrate having a second top surface and a second bottom surface opposite the second top surface, a thermoset ink disposed between the first substrate and the second substrate; and an adhesive forming at least part of a gap extending from the first bottom surface to the second top surface, wherein the thermoset ink is disposed radially inward of the adhesive along an axis of the FSR assembly extending substantially parallel to at least one of the first bottom surface and the second top surface.
An electronic device contains a processor, a display, memory, and a force-sensitive resistor (FSR) assembly connected to the processor. The FSR assembly includes two electrically insulating substrates. A thermoset ink is between the substrates. An adhesive forms a gap between the substrate surfaces. The thermoset ink is radially inward from the adhesive.
7. The electronic device of claim 6 , wherein the adhesive is in contact with the at least one of the first bottom surface and the second top surface and extends substantially around a perimeter of the at least one of the first bottom surface and the second top surface.
The electronic device with the FSR assembly as described previously has the adhesive in contact with at least one of the substrate surfaces and extends around the perimeter of that surface, securing the substrates together while also defining the sensing area within the perimeter.
8. The electronic device of claim 6 , wherein the adhesive is radially spaced from the thermoset ink along the axis.
The electronic device with the FSR assembly as described previously includes an adhesive that is radially spaced from the thermoset ink. This spacing creates a defined sensing area and prevents the adhesive from interfering with the electrical properties of the thermoset ink.
9. The electronic device of claim 6 , wherein the thermoset ink comprises a first portion disposed on the first bottom surface and a second portion disposed on the second top surface, and wherein the first substrate is spaced from the second substrate such that the first portion is separated from the second portion by a distance.
The electronic device with the FSR assembly as described previously includes thermoset ink with two separate portions; one on the first substrate's bottom surface and one on the second substrate's top surface. The first and second substrates are separated such that the two ink portions do not touch.
10. The electronic device of claim 9 , wherein the first substrate is configured to flex in response to application of force, and wherein flexing of the first substrate varies the distance between the first and second portions.
In the electronic device with the FSR assembly as described previously, the first substrate can bend when force is applied. As it bends, the gap between the two ink portions changes, altering the resistance measured by the FSR and providing the force sensing capability.
11. The electronic device of claim 6 , wherein the thermoset ink is embedded within one of the first substrate or the second substrate.
The electronic device with the FSR assembly as described previously has the thermoset ink embedded within one of the substrates. This could provide mechanical protection and improved durability to the ink layer.
12. The electronic device of claim 6 , wherein: the thermoset ink comprises a first thermoset ink and second thermoset ink, a single layer of the first thermoset ink is disposed on substantially the entire first bottom surface of the first substrate, and a single layer of the second thermoset ink is disposed on substantially the entire second top surface of the second substrate.
The electronic device with the FSR assembly as described previously contains first and second thermoset inks. A single layer of the first thermoset ink is disposed on the entire first substrate surface, and a single layer of the second thermoset ink is disposed on the entire second substrate surface.
13. The electronic device of claim 6 , the thermoset ink having one or more of: a curing temperature between approximately 150° Celsius and approximately 350° Celsius, or an electrical resistance between approximately 16 kΩ/mm2 and approximately 29 kΩ/mm2.
The electronic device with the FSR assembly as described previously utilizes thermoset ink with either a curing temperature between 150°C and 350°C or an electrical resistance between 16 kΩ/mm2 and 29 kΩ/mm2, to achieve desired performance and manufacturability.
14. The electronic device of claim 13 , the electrically insulative material having one or more of: a decomposition temperature greater than or equal to approximately 300° Celsius, or a coefficient of thermal expansion less than or equal to approximately 30.
In the electronic device containing the FSR assembly as described previously, the electrically insulating material possesses either a decomposition temperature of at least 300°C or a coefficient of thermal expansion of at most 30 to ensure high reliability in harsh operating conditions.
15. The electronic device of claim 6 , the thermoset ink comprising at least one of carbon black particles and silver particles, the at least one of the carbon black particles and the silver particles each having a particle size between approximately 70 nanometers and approximately 2 micrometers.
The electronic device with the FSR assembly as described previously has thermoset ink with carbon black or silver particles, with each particle being between 70 nanometers and 2 micrometers in size.
16. The electronic device of claim 6 , further comprising a preload layer, and a force concentration layer disposed between the preload layer and the first top surface, the preload layer applying a preload force to at least one of the first substrate or the second substrate, via the force concentration layer, between approximately 100 gram force and approximately 500 gram force in the absence of other external forces applied to the first substrate.
The electronic device including an FSR assembly as described previously also includes a force concentration layer and a preload layer. The preload layer applies a force (100-500 gram force) on the substrate via the force concentration layer when no other forces are applied.
17. A force sensing resistor (FSR) assembly, comprising: a first electrically insulative substrate, the first electrically insulative substrate having a first top surface and a first bottom surface opposite the first top surface; a second electrically insulative substrate, the second electrically insulative substrate having a second top surface and a second bottom surface opposite the second top surface; a thermoset ink disposed on at least one of the first bottom surface or on the second top surface; and a spacer disposed at least partly between the first and second electrically insulative substrates, the spacer forming at least part of a gap extending from the first bottom surface to the second top surface, wherein the thermoset ink is disposed radially inward of the spacer along an axis of the FSR assembly extending substantially parallel to at least one of the first bottom surface and the second top surface.
A force sensing resistor (FSR) assembly consists of two electrically insulating substrates each having a top and bottom surface. A thermoset ink is placed on at least one of the surfaces (bottom of first or top of second). A spacer is positioned partly between the substrates, creating a gap between the surfaces. The thermoset ink sits radially inward from this spacer.
18. The assembly of claim 17 , wherein: the thermoset ink comprises a first thermoset ink and a second thermoset ink different from the first thermoset ink, the first thermoset ink is disposed on the first substrate and the second thermoset ink is disposed on the second substrate, the spacer is disposed substantially around a perimeter of the least one of the first bottom surface and the second top surface, and the spacer is radially spaced from the first thermoset ink and the second thermoset ink along the axis.
The FSR assembly described previously utilizes two different thermoset inks, one on each substrate. A spacer runs around the perimeter of at least one of the substrate surfaces and is spaced radially apart from the thermoset inks. This provides mechanical support and defines the sensing area.
19. The assembly of claim 17 , further comprising: a force concentration layer disposed on at least a portion of the first top surface; and a preload layer disposed on the force concentration layer such that the force concentration layer is disposed between the preload layer and the first top surface, the preload layer applying a preload force to at least one of the first electrically insulative substrate or the second electrically insulative substrate, via the force concentration layer.
The FSR assembly described previously further incorporates a force concentration layer and preload layer. The force concentration layer resides on at least a portion of the first substrate's top surface. The preload layer is positioned on top, and applies a consistent force to the substrate via the force concentration layer.
20. The assembly of claim 17 , further comprising: a plurality of conductors disposed on the second top surface; and a dielectric material disposed on at least one conductor of the plurality of conductors such that the dielectric material is disposed between the first bottom surface and the at least one conductor.
The FSR assembly described previously includes a plurality of conductors on the second substrate's top surface. A dielectric material covers at least one conductor between the first bottom surface and the conductor, preventing electrical shorts and enabling precise control over the electrical properties of the sensor.
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August 26, 2014
May 30, 2017
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